Synchronization for facsimile transmission



March 10, 1931. 5, PURlNGTON 1,795,616

SYNCHRONIZATION FOR FACSIMILE TRANSMISSION Filed May 18, 1929 7 INVENTOR ELLISON S.PURING|ON ATTORNEY Patented: Mar. 10, 1931 UNITED STATES PATENT o1=1=1cE ELLISON S. ,PUBINGTON, 01 GLOUCESTER, MASSACHUSETTS ,'ASBIGNOR TO JOHN HAYS HAMMOND, JR.

BYNGHRONIZAT'ION FOR FAOSIMILE TRANSMISSION Application filed May 18,

In the transmission of facsimile, television, etc., it is necessary to have a moving rotary member, at the receiver, synchronized in its rotation with a similar rotary member, at the 5 trans'mitter. Various means areemployed in an attempt to perfect the mechanism for accomplishing synchronism between these rotary elements.

It is an object of this invention to permit I more nearly perfect synchronism between the rotary elements at the transmitter and receiver.

It is a further object of this invention to drive a rotary element in accordance with controlling master oscillations.

It is another object of this invention to drive a rotary element in accordance with impulses received from the transmitter.

A still further object of this invention is to provide a synchronizing arrangement which permits synchronization without the use of high speed contacts.

It is another object of this invention to synchronize by utilizing the phase relationships of the generated and controlled synchronizing frequencies rather than the amplitudes of the two frequencies.

It is an additional object of this invention to produce an arrangement for making the synchronization independent of fading of the incoming signal.

It is an additional object to provide a method of synchronization which will retain the motion of the two rotary members synchronous despite slight variations of speed of the controlling rotary member at the transmitter.

With the present method of synchronization for signals, utilizing impulses transmitted from the transmitter, absolute accuracy in the speed of the rotary member at the trans mitter is not so important as variations of one or two percent in the speed of the rotary element at the transmitter, will be taken care of by a similar variation in speed at the receiver so that the result will be practically unaffected by the original variations.

This arrangement for synchronizing without the use of high speed contacts, utilizes the action between the current produced by the 1929. Serial No; 364,224.

rotating machine, the speed of which it is desired to accurately control, and the current received from a standard, or preferably the frequency of a current received from the transmitter. This latter has the advantage of the synchronization not depending upon the amplitude of the pulsating current to the same .degree as in the other arrangements, and is therefore especially a plicable to synchronization by received radio impulses.

In order to render this system more independent of the intensity of the received radio impulses, there is provided a system for compensating for the loss in energy in the controlling current by an increase in the intensity of the current locally generated to keep constant the total of the interacting energies which control the speed of the motor.

In accomplishing this invention, a phase operated relay is provided, the alternating controlling current being fed to one of the windings of the relay, preferably the stator winding, and the alternating current produced by the machine, the rotation of which is to be controlled, being fed to the other winding of the relay, preferably the armature winding. A displacement of the armature windin relative to the stationary winding due to c ange in the phase of the current produced by the generator relative to that of the controlling current, causes the relay to operate to increase or decrease the speed of the driving motor by an appropriate amount to correct the phase displacement.

Having thus briefly described my invention, attention is invited to the drawings in which:

Fig. 1 is a diagram showing the circuit for carrying out my invention;

Fig. 2 is a schematic drawing of a phase operated relay which may be utilized at the circuit shown in Fig. 1 to correct the speed of the driving motor as required; and,

Fig. 3 is a circuit showing means for compensating for variations in the intensity of the received signal.

Referring now more particularly to Fig. 1, there is shown a motor generator comprising the direct current motor 1, and the alternating current generator 2. This motor is adapted to drive the apparatus, the speed of which it is desired to accurately synchronize relative to the s eed of a similar moving part at the transmltter. The direct current motor is supplied from a direct current source through the conductors 3, and is provided with a shunt field 4 and an auxiliary field 5. The current flowing through the shunt field 4 is adjusted in the usual manner by means of the rheostat-6.

The output of the alternating current generator passes through the primary 7 of the transformer 8 the secondary of which is connected to the rotary winding 10 of a phase 0perated relay, the construction of which will be more clearly set forth hereinafter.

The stationery or field winding 11 of the phase operated relay is supplied through the conductors 12. Actuated by the rotary coil 10 of the base indicator is the armature 13 which is apted to alternatively close thecontacts '14 or 15, depending upon the direction of the partial rotation of the rotary coil 10. For damping the motions of the armature there are provided the springs 16 and 17 The auxiliary field 5 of the direct current motor 1 is supplied by current from either the power source 18 or 19, in accordance with which of the contacts 14 or 15 are closed, which latter depends upon the motion of the rotary coil 10. When the contact 15 is closed, for instance, the current flowing through the coil..5 will be in the opposite direction from that which will flow through the same winds ing in case the contact 14 is closed. For preventing sparking of the contacts 14 and 15, there are provided the condensers 20 and 21,

connected in the usual and well known man ner.

The phase operated relay may be constructed as shown more particularly in Fig. 2 to which attention is now invited. The stationary windings may be mounted upon a field structure such as of a series wound alternating current motor, and in this instance comprising the two windings 11 mounted upon the field structure 120. The rotary coil may comprise the rotary or armature coil 10 mountedupon the armature core 121. Springs may be attached to prevent complete rotation and dampen the vibrations of the armature under varying phase displacements between the currents supplied to the field and armature coils. An arrangement is connected with the armature core 121 to operate the contacts 14 and 15 dependin upon the direction of the partial rotation o the armature.

Attention is now more particularly invited to Fi 3. The pulsing current for controlling t e rotation of the direct current motor is supplied, as has been above stated, from the transmitting station and this current is therefore subject to. fading, and other irre larities of transmission and reception. 1; may

therefore be necessary to provlde some means change in total excitation ofthe phase displacement due merely to change in received signal intensity. In accomplishing this resu t, the current generated by the alternating current generator 2 and supplied through the primary 7 and secondary 9 of the transformer 8 is supplied to the rotary winding 10, after being amplified by the amplifier 30; The

amplifier 30 consists of a thermionic device of ordinary structure, the filament of which ma be su plied by the source 31 in the usual an well Enown manner. The plate circuit of the amplifier 30 comprises the primary 33 of the transformer 35 and the high potential source 34. Inductivelycoupled to the pri mary 33 of the transformer 35 is the secondary 36 which is connected to supply the amplified locally generated alternating current to the rotary coil 10 of the phase operated relay. The locally generated current is impressed upon the grid of the amplifier device 30 by means of the circuit comprisingthe grid, the secondary 9 of the-transformer 8 the biasing resistor 43, and the filament of the amplifier device 30. The bias of the said resistor is varied in accordance with the incomin signal intensity as amplified by the ampli er 37 The incoming alternating current frequency is impressed across the grid filament of the amphfier device 37 throu h the biasing source 38. For supplying t e high voltage potential to the plate circuit of the amplifying device 37, there is provided the a. 0. source 44-which is adapted to sup-.

ply the primary winding 41 of the transformer 45, the secondary 39 of which is included in the plate circuit of said device. The secondary 39 is bypassed by the bypass condenser 40. The biasing resistor 43 is included in the plate circuit of the amplifier device 37 and is shunted by the bypass condenser 42. Thus, changes in the incoming si al will serve to vary the bias upon the gr1d of the amplifier device 30 and thus vary the amplification of the locally produced alternating current supplied through the amplifying device 30 to the winding 10. Adjustment may be made so that the increase or decrease in received current may be exactly compensated by the corresponding decrease or increase in the amplification of the locally produced alternating current, in the amplifier device 30.

Having thus described my invention, I will now briefly describe its operation.

The motor which is adapted to rotate the ICC receiving reproducing apparatus is also adapted to produce an alternating current, the fre uency of which is the same as that of the a ternating current being transmitted by the transmitter. The incoming impulses serve to excite one of the windings of a phase operated relay and the locally generated impulses serve to excite the other winding of the same relay. The moving coil of the phase operated relay will seek to maintain itself in such a osition that there will be no current trans ormation between the rotary, coil and the stationary coil. This will require phase displacement of 90 between the current in the stationary and the rotary windings. If the speed of the motor 1 is slightly greater than that required to generate theproper frequenc there will e precession of the phase of t e current in the rotary winding 10 which will cause a rotation of the armature and will close one of the contacts 14 or 15 which, in turn, will cause a current to fiow through the auxiliary field winding 5 of the motor, in'such a direction that the flux produced by the said auxiliary winding will assist the flux produced by the shunt winding 4 and slow the rotation of the motor and therefore the generator. If, on the other hand, the motor becomes slightly too slow, there will be a precession in the phase of the field windings in the opposite direction to close the appropriate contacts 14 or 15 to cause the current to flow through the auxiliary winding 5 in the opposite direction and produce a ux which will oppose the flux produced by the shunt winding 4, and thus increase the speed of the rotation of the motor 1. For large changes in speed of rotation of the motor 1, the shunt field rheostat 6 is utilized in the usual manner, and the final small changes in speed required due to slight changes in the d. 0. supply or slight changes in the frequency received from the transmitter will cause the speed of rotation of the motor to increase or decrease by a corresponding amount to cause the generator to produce the proper alternating frequency.

For compensating for variations in the received signal intensity, the circuit shown in Fig. 3 is provided. The received current is rectified by the detector 37 and is adapted to vary the bias on the amplifier 30 which latter serves to amplify the locally produced current before it is supplied to the rotary coil 10. Thus, an increase in the received signal current will serve to increase the plate current of the detector 37, and thus increase the current produced through the biasing resistor 43, to increase the bias on the grid of the amplifier device 30, decreasing its plate current and therefore the amplification of the locally produced current occurring therein. Thus the current supplied to the winding 10 may be kept inversely in prois to be understood that I am not to be limited by the specific form of the invention shown and described for the purposes of illustration only, but by the scope of my invention as set forth in the appended claims.

I claim:

1. Means for the control of rotary motion for television and the like which comprises, a d. 0. motor, adapted to drive the rotaryinember the speed of which must be accurately controlled, and a. c. generator operatively connected to said motor, means for receiving controlling alternating current from a transmite ter having a rotary member with which the first mentioned roiary member is to be synchronized, aphase operated relay comprising a stator winding adapted to be excited by the received alternating current, a rotor winding adapted to be energized by the locally generated alternating current, contact means for said relay, said contact means being adapted to vary the strength of current in the field of said motor whereby the speed of the motor is so adjusted as to cause the locally generated current to be synchronous with the received current, and means for compensating for variations in the intensity of the received current comprising a rectifier for said received current, an amplifier for the locally generated current, and a biasing means for said amplifier controlled by the output of said rectifier.

2. Means for the control of rotation for television, facsimile reproduction, etc., which comprises, a variable speed (1. 0. motor, means operated by said motor for producing an alternating current, means for receiving a similar alternating current which is to control the speed of'rotation of said motor, a phase operated relay com rising, one winding adapted to be excited y the received alternating current, a second winding adapted to be excited by the locally generated our rent,'and contacts adapted to change the direction of the current flowing through an auxiliary field winding of said d. c. generator, thereby varying its speed to produce synchronism between the received alternating current and the locally generated alternat ing current, and means for maintaining the action of the phase operated relay constant despite fading in the received current which comprises an amplifier for the locally generated current, the bias of which is adapted to be varied in accordance with the intensity of the received alternating current.

3. Means for the control of a rotary member for use in television, facsimile reproduction, etc., which comprises, means for generating an alternating current directly pro- 1-, aromas ortional to the speed of the rotating repro- "gucing' device, means for supplying a controlling alternating current and means for comparing the phase of the locally generated and received alternatin currents, said means being adapted to contro the speed of the rotary member, and means for compensating for variations in the intensity of the received alternating current comprising means for rectifying said alternating current, means for amplifying the locally generated alternating current, and means for regulating the amount of amplification of said alternating current in accordance with the rectified received al-. ternating current.

4. The method of maintaining synchronism between sending and receiving members in television facsimile reproduction systems and the like which consists in generating an alternating current having a frequency directly related to the speed of the sending member nerating a like second alternating current aving a frequency directly related to the speed of the receiving member, transmitting said first current from the sending member to the receiving member, comparing said two currents, compensating for the variation in the intensity of the received current by varying the intensity of the current generated at m the receiving member so that the total energy of the two currents remains constant and varying the frequency of the current generated at the recelving member in accordance with the phase displacements of said two 5 currents.

ELLISON S. PURINGTON. 

